Lithologic control of ground-water flow and contaminant transport in a semi-arid environment, Tucson, Arizona

Tricloroethylene has been found in the ground water in south Tucson, Arizona, contaminating several water supply wells. The aquifer affected, characterized by water-table conditions, is comprised of upper and lower zones that merge in the northwest quadrant of the study area. A concealed block fault trends north-south in the center of the study area. East of the fault, the affected upper zone is comprised of sandy silts and silty sands; west of the fault, fairly consistent slightly silty sands and gravels. The lower zone, is comprised of weak to moderately cemented sands and gravels west of the fault. Regional hydraulic gradient is towards the northwest. Inflow into the study area originates as mountain front recharge from the south and infiltration from the Santa Cruz River to the west. The tricloroethylene, originating from several suspected source areas, appears to be following the general ground-water flow direction.hydrology collectio